Assessing the effectiveness of monitoring methods for Merlin Falcocolumbariusin Ireland: the Pilot Merlin Survey 2010 - UCC Ornithology Group
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Assessing the effectiveness of monitoring
methods for Merlin Falco columbarius in
Ireland: the Pilot Merlin Survey 2010
John Lusby*1, Darío Fernández-Bellon1, David Norriss2
and Alan Lauder3
1 BirdWatch Ireland, Midlands Office, Crank House, Banagher, Co. Offaly
2 National Parks and Wildlife Service, 7 Ely Place, Dublin 2
3 BirdWatch Ireland, Unit 20, Block D, Bullford Business Campus, Kilcoole, Co. Wicklow
* Correspondence author: jlusby@birdwatchireland.ie
Previous research and monitoring of Merlin Falco
columbarius in Ireland has been limited. This has
resulted in a lack of understanding of the status, trends
and ecology of the population. A Pilot Survey was
initiated in 2010 to assess the effectiveness of standard
survey methods applied to the Irish population, and to
inform an appropriate protocol for future monitoring.
Similar to a trial of methods conducted for the 1993-94
Merlin Survey in Britain, two survey elements were
undertaken simultaneously. Ten 3 x 3km squares were
independently surveyed between April and July 2010.
One group of surveyors (BWI) had no prior knowledge
of Merlin within the squares, whereas another group
(NPWS) possessed previous information on Merlin
occupancy. Results for both surveys were similar for six squares. BWI recorded a higher level of
breeding in two squares, while NPWS obtained more accurate detail on breeding status in two
squares. Combined results confirmed all squares to be occupied. Successful breeding was
confirmed in two squares. The findings emphasise considerable difficulties with monitoring Merlin
in Ireland. A high degree of variation in detection rates, plucking behaviour and mobbing
response was recorded, which affected the success of the methods employed. The average
number of Merlin signs located per square was 20.2, but ranged from 0-79. From 40 potential
mobbing events, only 12.5% resulted in responses from resident Merlin. A series of recommen-
dations for future research and monitoring are outlined.
Introduction this downward trend (B. Caffrey, pers. comm.). The
population fluctuations detected by the Breeding Birds Atlases
Previous research and monitoring of Merlin Falco (Sharrock 1976, Gibbons et al. 1993) have been the primary
columbarius in Ireland has been limited, resulting in an sources used to determine the categorisation of Merlin on the
absence of comprehensive data on distribution, abundance Amber list of Birds of Conservation Concern in Ireland (Lynas
and ecological requirements of the species. Evidence from the et al. 2007). However, due to difficulties associated with
Breeding Bird Atlases suggested a moderate decline in the detecting breeding Merlin, the survey methods employed by
breeding range of the Irish population (Sharrock 1976,
Gibbons et al. 1993), while preliminary results from the latest
Breeding Bird Atlas (2007-2011) highlights a continuation of Plate 61. Merlin (Shay Connolly).
Irish Birds 9: 143-154 (2011) 143
J.Lusby, D.Fernández-Bellon, D.Norriss & A.Lauder
Breeding Bird Atlases may not have provided a true indication driven by increases in sheep numbers on marginal upland
of the abundance, densities or distribution of the population. habitats as a result of EU grants to farmers in the 1980s and
In the absence of more comprehensive species specific 1990s (Fuller and Gough 1999). The pattern of widespread,
monitoring, sufficient data on the status and ecology of Merlin small-scale afforestation in Ireland, in contrast to more
necessary for the design and implementation of an effective extensive plantations in upland habitats in Britain, is also likely
conservation strategy is lacking. The Action Plan for Upland to be a factor which influences nest site choice. Norriss et al.
Birds in Ireland 2011-2020 (BirdWatch Ireland 2011) identified (2010) assessed Merlin breeding and nesting habitat at five
significant gaps in knowledge of the Irish Merlin population, traditional and geographically isolated sites in the late 1980’s.
as well as the necessity to establish baseline data and conser- Of 28 confirmed nests, all were located in old Hooded Crow
vation priorities for the species. Merlin are an Annex 1 species Corvus cornix nests, the majority (n = 26) of which were in
on the European Birds Directive 2009/147/EC (OJEU 2010), conifer plantations. McElheron (2005) conducted one of the
and there is a requirement to address these issues to afford most comprehensive studies on Merlin in Ireland by
the species the appropriate protection. monitoring populations on a long-term basis in the Wicklow
Breeding Merlin populations are typically associated with Mountains. Of 24 pairs recorded, only one pair nested on the
upland habitat types, where they occur in low densities ground, with another pair nesting on a large boulder. All other
(Hardey et al. 2009, Ayers and Anderson 1999). In Ireland they nest sites recorded as part of this study were located in trees,
have a widespread but sporadic breeding distribution the majority of which were associated with forest plantations.
(Gibbons et al. 1993). Due to numerous factors associated A survey in Connemara (Galway) located 12 breeding pairs,
with their nesting ecology and their discrete breeding of which only two pairs were ground nesting, both of which
behaviour, it is generally accepted that the Merlin is a difficult bred on densely vegetated islands on fresh water lakes
species to survey (Ayers and Anderson 1999). Three national (Haworth 1985).
surveys have been previously conducted in Britain. Due to Established survey methods for Merlin have been
concerns over population declines, a partial survey was successfully used in Britain and elsewhere to census predom-
initiated in 1983-84, followed by more comprehensive surveys inantly ground nesting populations (Hardey et al. 2009).
in 1993-94 (Bibby and Nattrass 1986) and in 2008, which also However, the variation in the breeding ecology of the Irish
included coverage in Northern Ireland (Ewing et al. in press). population has the potential to impact on the accuracy of
As part of the 1993-94 survey, trials were also conducted results when using these methods. A pilot survey in Ireland
to validate the methods employed. Six 3 x 3km squares were to test the effectiveness of established methods, as practised
surveyed by contract fieldworkers with no previous in Britain, was deemed appropriate in order to inform a
knowledge of Merlin within the survey squares. These squares practical and realistic protocol for future monitoring of the
were also simultaneously surveyed by local raptor fieldworkers population. Research on sign distribution, activity patterns
who had monitored breeding Merlin within these survey areas and mobbing behaviour was also carried out by BirdWatch
in previous years, and whose results were assumed to Ireland (BWI) to facilitate further insights into Merlin breeding
accurately reflect Merlin occupancy and breeding status in behaviour and the effectiveness of standard survey methods
each square. Results from both groups of surveyors were in detecting the species.
similar for all six squares, concluding that the methods
developed were likely to provide accurate estimates of Merlin Methods and study areas
in areas not previously surveyed (Rebecca and Bainbridge
1998). As in the trial of methods conducted as part of the 1993-94
Research findings in Ireland suggest a variation in the survey in Britain, two survey elements were undertaken
breeding ecology of the species in comparison to Britain. simultaneously. The BirdWatch Ireland (BWI) survey team
Although tree nesting has been recorded in Britain, predom- comprised experienced fieldworkers, which included
inantly in areas where suitable ground nesting opportunities experience of surveying raptors. However, this team had not
are limited (Bibby and Nattrass 1986), the majority of the previously worked on Merlin and had no previous information
British population is ground-nesting (Hardey et al. 2009). In on breeding Merlin in the selected survey squares. The
contrast, trees are the dominant nest site choice in Ireland National Parks and Wildlife Service (NPWS) survey team
(McElheron 2005, Haworth 1985, Norriss et al. 2010, (which included input from the Irish Raptor Study Group)
Fernández-Bellon et al. 2010), which is likely to be influenced covered the same squares. In contrast, these surveyors
by the limitation of heather cover of sufficient quality to possessed knowledge of Merlin within the survey squares,
provide optimal ground nesting opportunities. There has including the locations of previous nest sites. Both survey
been a major decrease in heather cover over the past century elements were carried out over the same time frame but were
in Ireland (Bleasdale 1998), with such changes being partially otherwise independent. The findings of both surveys were
144 Irish Birds 9 (2011)
Effectiveness of monitoring methods for Merlin in Ireland
then compared in order to highlight the success, included open water, urban areas, farmland, enclosed pastures
shortcomings and requirements of the survey techniques for and areas above 700m (Hardey et al. 2009). The remaining
future work. areas representing suitable Merlin habitat, including heather
Ten 3 x 3km squares were selected for the pilot survey. and grass moorland, forestry and bracken (Hardey et al. 2009)
Survey squares were chosen by NPWS, based on previous were intensively and systematically searched for signs of
knowledge of nest sites and distribution of NPWS surveyors. Merlin activity on the first visit.
All squares were suitable for breeding Merlin, were occupied
in previous years and were expected to hold at least one Sign searching
breeding pair. Squares were located in three counties, with
two squares in Wicklow, three in Galway and five in Donegal. All prominent features (boulders, hummocks, posts, etc.)
The locations and names of the selected survey squares are which could be used as perches by Merlin were checked for
shown in Figure 1. A practical workshop of survey techniques signs of activity (plucking remains, moth wings, white wash,
was held over two days at known Merlin sites in the Slieve pellets, moulted feathers, etc.). Hardey et al. (2009) and
Bloom and Wicklow Mountains on the 19 and 20 March 2010. Gilbert et al. (1998) recommend walking within 500m of all
This ensured a sufficient level of expertise among all points of suitable habitat when searching for evidence. For
fieldworkers involved. Survey work was carried out over four the pilot survey this distance was reduced to 200m to increase
months from 1 April to 31 July 2010. the likelihood of locating signs left by tree-nesting Merlin,
which can be more difficult to detect than the signs of ground
nesting pairs (Little and Davison 1992, Newton et al. 1984).
Norriss et al. (2010) noted the tendency of some tree nesting
pairs in Ireland to avoid plucking on the ground in favour of
branch perches, meaning open ground searches are less likely
to be successful in locating signs.
All signs located were assigned an individual reference
number and a ten-figure grid reference. The type of sign
(plucking, moth wings, etc.), perch type, number of prey and
age of sign estimated by assessing condition, deterioration
and weather exposure (previous season, more than three
weeks old, or less than three weeks old) was recorded. All
signs left by other raptor and corvid species were also
recorded. To determine variation in abundance and distri-
bution of signs between sites, and to assess the reliability of
sign searching as a method for confirming Merlin occupancy,
all recorded signs were mapped using ArcView and Mapsource
Figure 1. Location of the ten 3 x 3km Pilot Merlin software for each square. Research in Britain has shown that
Survey squares. as the breeding season progresses, Merlin pluckings and signs
tend to concentrate in the vicinity of the nest site, and can
therefore aid nest finding (Newton et al. 1994, A. Heavisides,
pers. comm.). The quantity of seasonal signs located within a
BWI survey methods
200 and 500m radius of all confirmed breeding attempts was
The BWI survey methods were primarily based on Hardey et determined.
al. (2009). Two fieldworkers made four visits to each square Any encounters with Merlins during sign searching were
between April and July 2010. Survey forms were used to logged as a casual encounter. These were assigned an
record the date, visit number, surveyors present, distance individual reference number and ten-figure grid reference of
walked and start and finish times of each visit. Weather the bird’s position. The type of encounter (visual observation
variables were recorded by assessing visibility, rain, wind and or calls), bird involved (male, female, juvenile or unknown)
cloud cover (assigning each a value of 1-3). The habitat and time and behaviour (flying in transition, perched, hunting,
composition of each square was assessed via aerial preening, mobbing other species, delivering prey to the nest,
photographs with further assessments made on foot or by calling, etc.) was recorded. Sightings of other species (e.g.
vehicle on the initial visit. Areas not considered suitable for corvids, herons, raptors, etc.) which might stimulate mobbing
breeding Merlin were identified on 1: 50,000 Ordnance Survey behaviour by Merlin were noted.
maps and excluded from further survey effort. These areas
Irish Birds 9 (2011) 145
J.Lusby, D.Fernández-Bellon, D.Norriss & A.Lauder
Vantage point watches forest in Glenveagh (Donegal) on 3 June and 5 July 2010.
These dates corresponded to the incubation and fledging
Once areas of Merlin activity were located from sign searching, period of the breeding cycle respectively. A third full day watch
vantage points were selected overlooking suitable nesting was undertaken on 18 June 2010 at a nest on an island in the
habitat as defined by Hardey et al. (2009), as well as nesting Kinvarra (Galway) survey square. Based on the behaviour of
habitats detailed in accounts of breeding Merlin in Ireland this pair, it is likely that this watch coincided with the pre-
(McElheron 2005, Haworth 1985, Norriss et al. 2010). These laying period. However, this cannot be confirmed as this
included forest edges, moorland with heather 30-70cm high attempt failed later in the season. Weather variables were
(Hardey et al. 2009, McElheron 2005, Norriss et al. 2010), recorded every hour to evaluate the relationship between
islands with dense vegetation or potential corvid nests Merlin activity and weather patterns. All Merlin sightings, calls
(Haworth 1985) and crags and rock faces (D. Norriss, pers. and behavioural observations were noted.
comm.). Particular attention was paid to passing corvids, To assess the benefits of utilising Merlin mobbing
herons, raptors and other species likely to elicit a mobbing behaviour as a survey tool, all potential mobbing events during
response from Merlin (Hardey et al. 2009). the full day watches were noted. A potential mobbing event
Previous studies recommended vantage point watches of was defined as an observation of corvids, gulls, herons or
two hours (Rebecca and Bainbridge 1998, Gilbert et al. 1998) raptors, either in flight or perched, within a radius of 50m of
or four to six hours duration (Hardey et al. 2009). For the BWI a Merlin or an active Merlin nest site. Merlin responses to the
element of the pilot survey, watches were carried out for a presence of any species in these groups were recorded to
minimum of three hours. Hardey et al. (2009) also assess the benefits of this method in locating occupied nesting
recommended carrying out watches in the morning or areas for future work.
evening to coincide with peak periods of activity. For the BWI
survey watches were initiated before 10:00 or after 16:00. In
squares where no signs were found, or where there were no Classification criteria
obvious areas of Merlin activity, vantage points were selected The criteria used to classify the status of each survey square
to cover all potential nesting habitat within the square. All was based on Hardey et al. (2009), incorporating modifi-
vantage points were assigned a unique reference number and cations to adjust for the ecology of the Irish Merlin population
a ten-figure grid reference and start and finish times were also (McElheron 2005, Haworth 1985, Norriss et al. 2010). Non-
logged. Any observations of Merlin or other species were breeding was excluded due to the difficulty in differentiating
recorded in a similar manner to casual encounters. If vantage it from failed breeding. Therefore the following four categories
point watches revealed new information which might be were used for the pilot survey:
enhanced by further watches, these were also carried out on
the same visit. Unoccupied: Fresh signs recorded on a single visit or no
sightings or calls recorded throughout the season.
Repeat visits
Occupied: At least one Merlin seen or heard, or fresh signs of
On subsequent visits (May, June and July) all perches holding occupation (pluckings, pellets, droppings or moulted Merlin
signs on the first visit were checked for renewed activity, and feathers) found on at least two occasions separated by at least
areas of known activity were searched for new signs. Vantage one week.
points were modified based on any new and relevant
information (new signs, encounters, etc.). Squares where Breeding attempt: Courtship display, alarm calling, copulation,
information was considered incomplete after four visits were eggs or eggshells found, young seen or heard.
visited a fifth time to increase the level of knowledge of the Successful breeding attempt: At least one young fledged or
square (confirm fledging, failed breeding attempts, etc). capable of flight recorded.
Activity patterns and mobbing NPWS survey methods
behaviour
NPWS surveyors were not required to adhere to a defined
To assess Merlin activity patterns and the efficiency of survey protocol. Alternatively, they relied on previous
detection rates from vantage point watches in relation to their monitoring experience within the selected squares to
timing and duration, three full day (dawn to dusk) watches determine the best means of assessing Merlin activity. All visits
were also carried out at two known nest sites. Two watches were carried out over the same time period as the BWI survey
were carried out at a confirmed nest site in a small block of (April-July) by a team of eight surveyors. The number of visits
146 Irish Birds 9 (2011)Effectiveness of monitoring methods for Merlin in Ireland
required in order to obtain accurate information on The average number of fresh signs recorded in the ten
occupancy and breeding status was left to the discretion of survey squares was 20.2, but varied significantly between sites,
individual surveyors. In general, initial searches for signs were ranging from 0-79 signs per square. Two squares which held
undertaken in the vicinity of historical sites, followed by breeding attempts (one successful and one failed) showed a
watches covering areas of potential or expected activity. concentration of signs in proximity to the nest site, with more
Timing of vantage point watches were not standardised and than 15 fresh signs recorded within a radius of 500m of the
were carried out for as long as was deemed necessary (ranging nest. None of the remaining four sites which held breeding
from one to six hours). Surveys were less exhaustive and attempts (one successful, three failed) showed a similar sign
systematic when searching for field signs and more effort was distribution pattern, with less than five signs located per site
invested in vantage point watches. Surveyors were asked to within 500m of the nest, despite comprehensive and
categorise Merlin status in each square according to the same standardized searches.
criteria as above. Merlin encounters during sign searching were recorded
on 30 occasions. For two of the survey squares these
Results encounters represented the only sightings throughout the
season (as birds were not detected at these sites during
BWI survey vantage point watches).
Two surveyors required 845 hours, over 137 field days (1 April-
20 July 2010) to complete four visits to each of the ten survey Vantage point watches
squares. Surveyors walked a combined total of 1,049km within
the survey squares over the course of the field season. A total of 97 vantage point watches were undertaken by BWI
Parameters recorded indicate that weather conditions (an average of 9.3 per square), each lasting a minimum of
were in general favourable for Merlin survey work. Of 112 field three hours, with the longest extending to 5.5 hours. Merlins
days, 77% had little or no rain, there were showers on 22% of were recorded on 75 occasions, but these encounters were
days with heavy rain recorded on less than 1% of days. unevenly distributed across watches. A total of 21 watches
Similarly, only 22% of days were completely overcast, while yielded sightings, with no Merlin encounters recorded on the
the rest were intermittently cloudy (44%) or clear (34%). remaining 76 watches.
Strong winds were recorded on 5% of days, 54% were breezy, The initial full day watch at Glenveagh on 3 June
and the remaining 41% were calm. Visibility was mostly good (incubation period) recorded 14 Merlin encounters over a 17
(61% of the days), with only some days of intermediate (35%) hour period (04:45-22:15), 13 of which were observations and
or low (4%) visibility. one vocalisation. The female was recorded ten times, the male
four times, and an unidentified adult on one occasion (with
both birds sighted together on one occasion). No Merlin
Sign searching
activity was recorded during two three-hour periods (11:00-
A total of 412 Merlin signs were recorded at 366 individual 14:00 and 18:00-21:00) despite the fact that this nest was active
perches by BWI across all sites during the survey period. Of and subsequently successful.
these, 223 were classed as fresh or seasonal, while the The 5 July watch (fledging period) at Glenveagh,
remaining 143 were assigned to the previous season or older. conducted over a 17 hour period (04:45-22:15) yielded a total
Plucked avian prey items (n = 292) were the most abundant of 52 encounters, of which 29 were sightings and 23 were calls.
sign recorded, followed by moths wings (n = 68 individuals), The male was observed on 13 occasions, the female on four,
pellets (n = 26), probable Merlin white wash (n = 22), and the fledglings on 47 (on 12 occasions an adult was
moulted Merlin feathers (n = 3) and dragonfly wings (n = 1). observed with the fledglings). Despite showers and strong
Boulders were the most abundant perch type recorded (n = wind throughout the day, Merlin activity appeared to be
170), followed by hummocks (n = 120) and posts (n = 65), constant and independent of weather conditions.
with other features such as upturned roots, earth banks and A total of 22 Merlin encounters were recorded on 18 June
turf stacks also used (n = 11). Perches where more than one (pre-laying period) at Kinvarra, all of which were observations.
prey item was found, accounted for 31% of all signs (n = 103). Three of these were of an unknown adult, four were of the
Of these, 45 corresponded to signs where more than one pair male, and 15 were of the female. The distribution and timing
of moth wings was found, or where moth wings were found of Merlin encounters recorded during each of the full day
alongside plucked feathers. The majority of perches holding watches at both sites are shown in Figure 2.
more than one item (n = 43) were recorded in the squares
which held breeding attempts (n = 5) and were predomi-
nantly located close (less than 500m) to breeding sites.
Irish Birds 9 (2011) 147J.Lusby, D.Fernández-Bellon, D.Norriss & A.Lauder
Figure 2. The distribution and timing of Merlin encounters during three full day watches.
Mobbing behaviour Occupancy and breeding success
A total of 40 potential mobbing events were recorded during The ten squares surveyed by BWI were classified as follows;
the three full day watches. These events involved seven one was unoccupied, four were occupied and breeding
species; Grey Heron Ardea cinerea, Sparrowhawk Accipiter attempts were confirmed in five (one of which is likely to have
nisus, Merlin, Great Black-backed Gull Larus marinus, Lesser held two breeding attempts). Four of these were considered
Black-backed Gull Larus fuscus, Hooded Crow and Raven to be unsuccessful, with only a single square confirmed as
Corvus corax. Of these, five resulted in a mobbing response holding a successful breeding pair (Table 2).
from resident Merlin. Table 1 shows Merlin responses to each
of the potential mobbing events in relation to the species
involved.
Table 1. The response of Merlin to potential mobbing events.
Birds involved
Species Number of potential Number eliciting a
mobbing events response by Merlin Male Female Both
Grey Heron 10 2 - 1 1
Sparrowhawk 4 1 1 - -
Merlin 1 1 1 - -
Great Black-backed Gull 1 - - - -
Lesser Black-backed Gull 11 1 - 1 -
Hooded Crow 11 - - - -
Raven 2 - - - -
Total 40 5 2 2 1
148 Irish Birds 9 (2011)Effectiveness of monitoring methods for Merlin in Ireland
Table 2. Comparison of BWI and NPWS survey results.
Square BWI NPWS
Fresh signs Sightings Result Fresh signs Sightings Result
Duff Hill Yes No Occupied Yes No Occupied
Carriglaur Yes Yes (many) Two failed No Yes (many) Two failed
breeding attempts breeding attempts
Letterfir Yes Yes (1) Occupied Yes Yes (1) Occupied
Glenamaddy Yes Yes (1) Breeding attempt, Yes No Unoccupied
possibly failed
Kinvarra Yes Yes (many) Breeding attempt, Yes Yes (many) Breeding attempt,
failed failed
Ardara Yes Yes (many) Breeding attempt, Yes Yes Occupied
failed
Glenties Yes Yes (1) Occupied Yes Yes Successful breeding
Glenveagh Yes Yes (many) Successful breeding - Yes Successful breeding
Buncrana No No Unoccupied Yes Yes (1) Occupied
Burnfoot Yes Yes (2) Occupied Yes Yes (1) Occupied
NPWS survey surveyors were able to confirm a successful breeding attempt.
Table 2 shows a comparison of the results for both surveys.
NPWS surveyors spent an average of five and a half days in
each square and carried out an average of 8.3 watches (lasting
between one and six hours) per square to determine Discussion
occupancy or breeding status. The ten squares surveyed by
Survey comparisons
NPWS were classified as follows; one was unoccupied, five
were occupied and breeding attempts were confirmed in four. One of the most significant results of the pilot survey was the
Two of the squares with a confirmed breeding attempt were contrast in findings between the BWI and NPWS survey
considered to have failed (one with two failed attempts), and elements. This emphasises the difficulties associated with
two were considered to have held successful breeding pairs monitoring Merlin in Ireland, and also highlights specific
(Table 2). aspects that need to be addressed prior to establishing an
effective monitoring protocol. Results for both elements were
Comparing results from the two surveys similar for only six of the ten survey squares. BWI recorded a
higher level of breeding information in two squares, with
The BWI and NPWS survey results were similar for six squares NPWS also obtaining more accurate detail on breeding status
(Duff Hill, Carriglaur, Letterfir, Kinvarra, Glenveagh and in two squares. These findings indicate that even intensive
Burnfoot) with contrasting findings recorded for the and systematic survey work (BWI survey), or previous
remaining four. Buncrana was recorded as unoccupied by the experience of monitoring Merlin at traditional sites (NPWS
BWI survey, but was found to be occupied by NPWS. survey) cannot guarantee accurate determination of breeding
Conclusions on breeding status varied between the surveys status using the pilot survey methods. In contrast to the
in relation to the three remaining squares. At Glenamaddy and results of the current survey, similar trials undertaken as part
Ardara, BWI confirmed breeding attempts while NPWS of the 1993-94 Merlin survey in Britain revealed identical classi-
surveyors considered Glenamaddy to be unoccupied and fications for all six squares between the two teams of
Ardara to be occupied but did not record a breeding attempt. surveyors. This comparison highlights the potential variation
At Glenties, BWI surveyors recorded occupation while NPWS in effectiveness of established Merlin survey techniques
Irish Birds 9 (2011) 149J.Lusby, D.Fernández-Bellon, D.Norriss & A.Lauder
between Britain and Ireland, and the necessity for further determining occupancy and breeding status between sites.
research on Merlin monitoring methods in the Irish context. Sign searching and vantage point watches are the standard
There are numerous potential factors responsible for the methods used for surveying Merlin throughout their range,
disparity in results between the BWI and NPWS survey and were the primary methods employed by the BWI survey.
elements compared with the trials conducted as part of the Both methods proved to be valuable survey tools, but the
1993-94 Merlin survey in Britain. Firstly, the level of Merlin merits of each in detecting Merlin varied greatly between
monitoring in Britain is more comprehensive than in Ireland. squares.
The raptor workers involved in the British trials had an
intimate knowledge of the Merlin in their survey areas. NPWS Sign searching
surveyors possessed a similar level of knowledge for certain
squares, but other squares had only received sporadic Sign searching provided confirmation of occupancy in seven
monitoring in recent years. squares in the BWI survey. Evidence of fresh signs on visits
The year 2010 was considered a poor one for breeding separated by a week or more, in addition to casual encounters
Merlin, and this may potentially explain some of the variation provided the final survey results for six squares. However the
in results between the survey elements. Lower breeding pilot survey also identified the unreliability of sign searching
success rates were recorded in 2010 in comparison to the for determining occupancy and for locating nests in certain
findings of Norriss et al. (2010) who assessed breeding situations. The dominance of tree nesting in Ireland is likely
parameters of the species between 1986 and 1992. Non- to impact on the effectiveness of this method compared with
breeding birds are less likely to restrict their movements or Britain, where the majority of pairs nest on the ground
plucking activity to specific areas or to engage to the same (Hardey et al. 2009). In a study in Northumberland, Little and
extent in behaviour (mobbing, courtship display, calling etc.) Davison (1992) found that tree-nesting birds tend to pluck on
which may facilitate locating a breeding pair (Newton et al. branches, which makes the location of both signs and nests
1984, A. Heavisides pers. comm.). Therefore, it is to be more difficult. Newton et al. (1984) noted that prey remains
expected that survey methods are less efficient at detecting are more evident around Merlin nests surrounded by heather
non-breeders. It is likely that a reduction in passerine prey in moorland compared with nests which are surrounded by
typical upland Merlin sites was responsible for low breeding grassland or forestry, which are generally the dominant habitat
success in 2010, with only two successful nesting attempts types associated with Merlin breeding sites in Ireland. Norriss
recorded at ten 3 x 3km pilot survey squares. Studies have et al. (2010) also commented on the difficulties in locating
indicated that breeding Merlin densities are likely to be related nests at disturbed sites, or sites bordering grassland, as
to prey density and abundance (Wiklund 1996, Wiklund and plucking tended to be carried out in the tree canopy. Without
Larsson 1994). the aid of signs to narrow the search, survey efficiency was
The 2009/10 winter was one of the most severe in 50 years reported to drop from 87% to 60% in this study.
(Met Éireann 2010), and this is likely to have resulted in a The BWI sign searching methodology was more intensive
reduction in certain passerine populations. Preliminary results and systematic than the methods used or recommended in
from the Countryside Bird Survey (CBS) (Coombes 2010) and previous studies (Hardey et al. 2009). Despite the fact that all
Breeding Bird Atlas 2007-2011 (B. Caffrey, pers. comm.) ten survey squares were confirmed to be occupied, there was
indicate severe declines in some upland species, such as a very low number of signs located within certain squares. Less
Meadow Pipit Anthus pratensis and Stonechat Saxicola than 20 seasonal signs were recorded in six individual squares.
torquata. These species are known to be important prey of One square (Burnfoot) only held a single fresh sign and one
the Merlin (Rae 2010, McElheron 2005, Rebecca 2004, Clarke seasonal sign, with another square (Buncrana) yielding no
and Scott 1994, Bibby 1987, Newton et al. 1984, Watson 1979). signs at all. Based on sign searching alone and the criteria
The pilot survey methods would, therefore, be expected to used, both squares would have been classed as unoccupied.
be more effective in a typical Merlin breeding season with Therefore negative results from comprehensive sign searching
higher numbers of successful breeding pairs. in suitable habitat cannot definitively rule out Merlin
However, the most likely factors impacting the occupancy. Further research is required to assess the specific
effectiveness of the pilot survey methods relate to the nesting aspects which influence Merlin plucking behaviour in the Irish
ecology and breeding behaviour of Merlin in Ireland. The context, which would allow greater confidence in this method
findings of the pilot survey indicate a high degree of variation based on the characteristics of individual sites.
between sites in relation to breeding ecology, sign distri- The distribution of signs with respect to nest sites was
bution, plucking and mobbing behaviour, which is probably also highly variable between sites. Of the four sites where
driven by habitat and nest site characteristics. This resulted in failed breeding attempts were recorded, only one (Ardara)
a significant difference in the efficiency of survey methods for produced more than 15 signs within 500m of the nest.
150 Irish Birds 9 (2011)Effectiveness of monitoring methods for Merlin in Ireland
Plate 62. Merlin (Shay Connolly)
However, McElheron (2005) suggested that sign patterns only 2009) therefore, observations around nest sites may be
become evident once clutches are complete. As the stage at restricted. This is accentuated when birds’ nest within fire
which these four attempts failed remained unknown, it is not breaks in plantations or away from the forest edge. Norriss et
possible to fully analyse the merits of nest finding based on al. (2010) recorded 72% of nests (n = 61) within 60m of the
sign distribution at these sites. Of the two successful sites, forest edge, and also recorded four nests which were over
only one (Glenveagh) followed a pattern of sign distribution 250m from the forest edge. Results from the vantage point
which allowed relative ease of confirmation of occupancy and watches conducted during this survey suggest that watches at
which aided the subsequent locating of the nest. At Glenties, nests in more ‘open’ habitats, such as open woodland, islands,
the other successful site, a similar sign distribution pattern small blocks of forest or shelter belts, yield more encounters
was not evident. This further indicates sign searching to be a than nesting sites in more ‘concealed’ habitats, such as large
beneficial survey tool for locating certain pairs, but for other and dense forest plantations. However it is not possible to
pairs this method is significantly less effective. comprehensively analyse this aspect with the current dataset
due to the small sample sizes and high degree of variation
Vantage point watches between the habitat characteristics of each site.
The BWI survey carried out six watches on three active
Vantage point watches provided specific information nests without any observations. This stresses the discrete
regarding the breeding outcome in five squares. Merlins nature of the species and reinforces the fact that absence of
nesting in forests tend to select concealed nests (Sieg and breeding Merlin cannot be determined from negative results.
Becker 1990) which are seldom directly visible (Hardey et al. In relation to the required timing and duration of vantage
Irish Birds 9 (2011) 151J.Lusby, D.Fernández-Bellon, D.Norriss & A.Lauder
point watches, it must be noted that no Merlin encounters however, that given the low breeding success recorded, the
were recorded over two three-hour periods (11:00-14:00 and 2010 season was regarded as an exceptionally poor breeding
18:00-21:00) on a full day watch on 3 June at Glenveagh, year for Merlin, and that time constraints may be a less
despite the fact that watches focused on the active nest area. significant issue in a more productive year. Regardless, the
These watches were within the time frame recommended by time, fitness, experience and motivation required of surveyors
Hardey et al. (2009), indicating that the duration of vantage in order to achieve accurate results must be taken into
point watches should be extended beyond three hours to account when devising a future realistic survey or monitoring
afford greater confidence in the results. In common with sign protocol for Merlin in Ireland, particularly in light of the
searching, further research is needed on how the success of limited raptor fieldworker resources.
vantage point watches vary between Merlin sites, and the
determining factors which influence this is recommended. Recommendations for future work
Vantage point watches are labour intensive and produce poor
detection rates in certain situations. Therefore, we The Merlin is an Annex I species on the European Birds
recommend that the broadcasting of Merlin calls, which has Directive 2009/147/EC (OJEU 2010), and is Amber-listed on
been used with some degree of success in other parts of the the Birds of Conservation Concern in Ireland (Lynas et al.
species range (Ayers and Anderson 1999, Doolittle and 2007). Due to the lack of information on Merlin population
Balding 1995), should be considered in Ireland. parameters in Ireland, it is recommended that the priority
focus for future work should be to determine population
Mobbing status and trends. The urgency for obtaining such data is
accentuated by the results of this study in conjunction with
Merlin territorial behaviour, including aggressive defence of evidence from the latest Breeding Bird Atlas (B. Caffrey, pers.
the nesting area from a range of species including corvids, comm.), which indicate that Irish Merlin populations may be
herons and other raptors can be useful in locating occupied undergoing at least short-term declines. Monitoring of
territories and nest sites. Hardey et al. (2009) recommend breeding parameters at key sites was continued in
close observation of such species in the proximity of potential 2011(Fernández-Bellon and Lusby 2011). Merlin breeding
or known Merlin sites during the breeding season to aid success values combined for 2010 and 2011 were 0.7-1.3
identification of occupied territories and nesting locations. fledglings per breeding attempt (n = 14), which is significantly
However, the findings from the three full day watches carried lower than those reported by previous studies of stable or
out in 2010 show that although Merlin mobbing behaviour increasing populations. These results are similar to the
can assist in locating breeding sites, the rates of response were findings of Meek (1988) and Roberts and Green (1983). These
low. Only 12.5% of all potential mobbing events resulted in a authors reported marked population declines in Orkney and
response by breeding Merlin. Similar to other methods used Wales, respectively, and the productivity figures are lower than
for locating breeding Merlin (sign searching and vantage point required for a population to remain stable (2.2-2.6 fledglings
watches), negative results from potential mobbing events per breeding attempt) (Bibby and Nattrass 1986, Rebecca et al.
therefore do not guarantee absence of breeding Merlin. 1992). All of this is indicative of short-term declines in the Irish
population. In the Irish context, breeding success and produc-
Fieldworker requirements tivity are markedly lower than recorded by previous work
carried out in 1986-92, when populations were considered to
In addition to the difficulties outlined above, the time be stable (Norriss et al. 2010).
consuming nature and specific fieldworker requirements to It is clear that strategic monitoring of Merlin in Ireland is
achieve accurate survey results must also be taken into required in order to obtain sufficient data to inform and
account when planning a future monitoring scheme. implement an adequate conservation plan for the species. The
Substantial survey efforts were necessary over the course of pilot survey highlights significant difficulties associated with
the field season for a comparatively low return. The charac- surveying Merlin in Ireland, and suggests that implementation
teristics of the terrain and the methods employed required a of a national census of the Merlin population is likely to be
high level of physical fitness and motivation. The BWI survey overly ambitious at this stage. It is therefore recommended
was primarily undertaken by two fieldworkers, which required that efforts could be more effectively focused on compre-
four months to survey ten 3 x 3km squares. Weather hensive monitoring of key populations (particularly within
conditions were favourable for survey work for the majority of SPA networks) to assess densities, breeding success and
the season (over 95% of days were classified as suitable). trends over successive years. In addition, given the findings
Despite this there was insufficient time to accurately ascertain in relation to the unreliability of standard survey methods at
breeding status in a minimum of two squares. It must be noted detecting Merlin at specific sites, it is also recommended to
152 Irish Birds 9 (2011)Effectiveness of monitoring methods for Merlin in Ireland
assess the potential benefits of alternative survey methods. surveyors involved in the NPWS survey, including the surveyors from
Playback methods for detecting breeding have been used with the Irish Raptor Study Group for their intensive fieldwork efforts;
some success (Ayers and Anderson 1999, Doolittle and Anthony McElheron, Dermot McLaughlin (IRSG), Irene O’Brien,
Balding 1995), as have decoys (Warkentin et al. 1990, Doolittle Aonghús Ó Dónaill, Lorcan O’Toole (IRSG), Alyn Walsh and John
Wilson, and also Damian Carroll who worked as part of the BWI survey
and Balding 1995, Wiklund 1996), and both should be
team. Aonghús Ó Dónaill and Dermot Breen for assistance with
considered for future monitoring work. assessing Merlin activity patterns in Connemara. Triona Franks for her
As well as a lack of information on Merlin distribution and assistance in running the Midlands Office in Banagher. The support of
abundance in Ireland there is also a limited understanding of BWI staff in Banagher and Kilcoole, and also David Tierney (NPWS) for
the ecological requirements of the species, factors which his help and support.
impact on the population and conservation measures which
would benefit the population. Data on nesting ecology, References
including nest site availability, selection and the implications
of forestry management at key sites, as well as information on Ayers, L.W. & Anderson, S.H. 1999. Reoccupancy and use of historic
habitat requirements is essential. The provision of artificial breeding sites by Richardson’s Merlin (Falco columbarius
nesting sites, in the form of nest baskets, is a measure that has richardsonii) in Wyoming. Final report to Wyoming Cooperative
been implemented with success in other countries (Rebecca Fish and Wildlife Research Unit. University of Wyoming, Laramie.
1998, Ivanovski 2000). It is recommended that a strategic nest Bibby, C.J. 1987. Foods of breeding Merlins Falco columbarius in
Wales. Bird Study 34: 64-70.
basket scheme be initiated at suitable sites which would
Bibby, C.J. & Nattrass, M. 1986. Breeding status of the Merlin in Britain.
provide additional nesting options for the species where British Birds 79: 170-185.
natural sites may be limited, and also serve to facilitate more BirdWatch Ireland. 2011. Action Plan for Upland Birds in Ireland
detailed monitoring in future years. 2011-2020. BirdWatch Ireland’s Group Action Plans for Irish Birds.
In conclusion, the following recommendations are listed BirdWatch Ireland, Kilcoole.
in order of priority: Bleasdale, A. 1998. Overgrazing in the West of Ireland – assessing
• Strategic monitoring of key sites (particularly SPA’s) to solutions. In G. O’Leary & F. Gormley (eds). Towards a
determine Merlin densities, breeding success, productivity Conservation Strategy for the Bogs of Ireland. Pp 67-78. Irish
and movements over successive years to assess population Peatland Conservation Council, Dublin.
status and trends. Clarke, R. & Scott, D. 1994. Breeding season diet of the Merlin in
County Antrim. Irish Birds 5: 205-206.
• Implement and evaluate the conservation benefits of a
Coombes, D. 2010. Some birds scarce after long hard winter. Wings
nest basket scheme at key sites. 58: 13.
• Test the effectiveness of playback as a method for Doolittle, T. & Balding, T. 1995. A survey for the Eastern Taiga Merlin
detecting breeding Merlin. (Falco columbarius) in Northern Minnesota, Winsconsin and
• Assess the effectiveness of decoys for detecting breeding Michigan. The Passenger Pigeon 57: 31-36.
Merlin and for trapping Merlin for telemetry studies. Ewing, S.R., Rebecca, G.R., Heavisides, A., Court, I., Lindley, P.,
• Initiate a telemetry study to determine breeding home Ruddock, M., Cohen, S. & Eaton, M.A. 2011. Breeding status of
range sizes and habitat use in order to inform SPA Merlins Falco columbarius in the UK in 2008. Bird Study
management and conservation plans. DOI:10.1080/00063657.2011.606497.
• Expand on previous dietary studies to facilitate an Fernández-Bellon, D., Carroll, D. & Lusby, J. 2010. Pilot Merlin Survey.
understanding of diet and prey requirements in relation to Report to the National Parks and Wildlife Service. BirdWatch Ireland,
Banagher.
habitat use.
Fernández-Bellon, D. & Lusby, J. 2011. Irish Merlin Ecological
Research, 2011 Report. Report to the National Parks and Wildlife
Acknowledgements Service. BirdWatch Ireland, Banagher.
Fuller, R.J. & Gough, S.J. 1999. Changes in sheep numbers in Britain:
The Pilot Merlin Survey was funded by the National Parks and Wildlife implications for bird populations. Biological Conservation 91: 73-
Service, of the Department of the Environment, Heritage and Local 89.
Government, with additional contribution to costs from BirdWatch Gibbons, D.W., Reid, J.B. & Chapman, R.A. 1993. The New Atlas of
Ireland. The authors of this paper would like to extend their special Breeding Birds in Britain and Ireland: 1988-1991. Poyser, London.
thanks to the following people for their assistance with various aspects Gilbert, G., Gibbons, D.W. & Evans, J. 1998. Bird Monitoring Methods.
of the pilot survey; Ken Shaw and Anthony McElheron for leading the RSPB, Sandy.
survey workshop and Jason Monaghan who assisted with the workshop Hardey, J., Crick, H., Wernham, C., Riley, H., Etheridge, B. &
in the Slieve Blooms. All workshop attendees; Damian Carroll, Alex Thompson, D. 2009. Raptors: a field guide for surveys and
Copland, Anthony McElheron, Jason Monaghan, Stephen Newton, monitoring. Stationery Office, Edinburgh.
Irene O’Brien, Aonghús Ó Dónaill, Ken Shaw, Alyn Walsh and Davy Haworth, P.F. 1985. A survey of upland breeding birds in west Galway,
Watson for their input and contributions. Thanks also to all the Éire. Report to the World Wildlife Fund Project.
Irish Birds 9 (2011) 153J.Lusby, D.Fernández-Bellon, D.Norriss & A.Lauder Ivanovski, V.V. 2000. Construction of artificial nests as a conservation Rebecca, G.W. 1998. Repeated use of an artificial crow nest by Merlins. measure for rare birds of prey. Buteo 11: 131-138. The Raptor 25: 22-24. Little, B. & Davison, M. 1992. Merlins Falco columbarius using crow Rebecca, G.W. 2004. Forest nesting Merlin apparently specialising on nests in Kielder Forest, Northumberland. Bird Study 39: 13-16. Barn Swallows. Scottish Birds 24: 46-48. Lynas, P., Newton, S.F. & Robinson, J.A. 2007. The status of birds in Rebecca, G.W. & Bainbridge, I.P. 1998. The breeding status of the Ireland: an analysis of conservation concern 2008-2013. Irish Birds Merlin Falco columbarius in Britain in 1993-94. Bird Study 45: 172- 8: 149-166. 187. McElheron, A. 2005. Merlins of the Wicklow Mountains. Currach Press, Rebecca, G.W., Cosnette, B.L., Hardey, J.J.C. & Payne, A.G. 1992. Status, Dublin. distribution and breeding biology of the Merlin in north-east Meek, E.R. 1988. The breeding ecology and decline of the Merlin Falco Scotland, 1980-1989. Scottish Birds 16: 165-183. columbarius in Orkney. Bird Study 35: 209-218. Roberts, J.L. & Green, D. 1983. Breeding failure and decline of Merlins Met Éireann. 2010. www.met.ie/climate/monthly_summarys/winter10.pdf on a north Wales moor. Bird Study 30: 193-200. Newton, I., Meek, E.R. & Little, B. 1984. Breeding season foods of Sharrock, J.T.R. 1976. The Atlas of Breeding Birds in Britain and Merlins Falco columbarius in Northumbria. Bird Study 31: 49-56. Ireland. British Trust for Ornithology, Hertfordshire. Norriss, D.W., Haran, B., Hennigan, J., McElheron, A., McLaughlin, D.J., Sieg, C.H. & Becker, D.M. 1990. Nest-site habitat selected by Merlins in Swan, V. & Walsh, A. 2010. Breeding biology of breeding Merlins south-eastern Montana. The Condor 92: 688-694. Falco columbarius in Ireland, 1986-1992. Irish Birds 9: 23-30. Warkentin, I.G. & West, N.H. 1990. Ecological energetics of wintering OJEU. 2010. EC Directive 2009/147/EC of the European Merlins Falco columbarius. Physiological Zoology 63: 308-333. Parliament and of the Council of 30 November 2009 on the Watson, J. 1979. Food of Merlins nesting in young conifer forest. Bird conservation of wild birds (codified version). Official Journal Study 26: 253-258. of the European Union L 20 (26 January 2010): 7–25. Wiklund, C.G. 1996. Determinants of dispersal in breeding Merlins http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:02 (Falco columbarius). Ecology 77: 1920-1927. 0:0007:0025:EN:PDF Wiklund, C.G. & Larsson, B.L. 1994. The distribution of breeding Rae, S. 2010. Prey items of Merlins in the Lewis Peatlands. Scottish Birds Merlins Falco columbarius in relation to food and nest sites. Ornis 30: 2-6. Svecica 4: 113-122. 154 Irish Birds 9 (2011)
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